52 F, H, Knowlton — Tertiary Floras of 



The older series of these lavas has been designated as the 

 early acid breccias and flows and the younger as the early basic 

 breccias and flows. Both these series of rocks carry plant re- 

 mains. In general, the matrix in which the plants are pre- 

 served is a fine-grained ash, probably deposited as a mud-flow, 

 in places with the appearance of stratification and other indi- 

 cations of waterlain deposits; occasionally the material is 

 much coarser and has the appearance of breccias mixed with 

 fine sediments. The acid rocks are usually light in color, 

 yellow, lavender, or gray, while the basic rocks which carry 

 more iron are darker in color, frequently some shade of green 

 or dark brown, passing over into black. In some instances, as 

 might be expected with fine waterlain beds, the deposits in both 

 series of lavas closely resemble each other, while the great mass 

 of lava of the two bodies may be readily distinguished. The 

 acid breccias, the oldest of the lava flows, rests in many places 

 upon the upturned edges of Archaean and Paleozoic rocks. In 

 most instances, the basic breccias either rest directly upon the 

 acid rocks, or else the underlying rocks are not exposed. The 

 acid breccias are found on both banks of the Yellowstone 

 Biver, below the mouth of Elk Creek. Again, near the 

 junction of Hell Roaring Creek with the Yellowstone River, 

 on Crescent Hill and near the head of Tower Creek. 



In the neighborhood of Lost Creek and on the northern end 

 of Specimen Ridge, along the drainage of Crystal Creek, the 

 basic breccias are known to lie directly upon the acid breccias. 

 In these localities the flora has a distinct character of its own, 

 and bears evidence of being younger than the flora from the 

 acid breccias. The basic series of rocks is typifled at the 

 Fossil Forest and also at the cliff a short distance to the south 

 and east of the Fossil Forest. They also occur on the east 

 bank of the Lamar River between Cache and Calfee Creeks. 

 All of these localities are characterized by their plant I'emains, 

 and the following determinations of age seem fully warranted. 



The Tertiary floras as above outlined are found to embrace 

 147 more or less satisfactory species. Of this number, 81 

 species, or over 50 per cent., have been described as new to 

 science. With these must be placed eight forms that have not 

 been speciflcally named, thus leaving 58 species that were be- 

 fore known, and upon which we must largely depend in the 

 determination of the age of the various strata in which they are 

 contained. 



The study of these plants has brought out the fact that they 

 may be naturally divided into three more or less distinct floras 

 or stages. These divisions, as already hinted in the remarks 

 concerning the geology of the beds containing them, correspond 

 with the geological divisions based upon the petrographical char- 

 acters of the rocks. The first or older fiora from the acid 



